Validation of stroke volume and cardiac output by electrical interrogation of the brachial artery in normals: assessment of strengths, limitations, and sources of error.

The goal of this study is to validate a new, continuous, noninvasive stroke volume (SV) method, known as transbrachial electrical bioimpedance velocimetry (TBEV). TBEV SV was compared to SV obtained by cardiac magnetic resonance imaging (cMRI) in normal humans devoid of clinically apparent heart disease. Thirty-two (32) volunteers were enrolled in the study. Each subject was evaluated by echocardiography to assure that no aortic or mitral valve disease was present. Subsequently, each subject underwent electrical interrogation of the brachial artery by means of a high frequency, low amplitude alternating current. A first TBEV SV estimate was obtained. Immediately after the initial TBEV study, subjects underwent cMRI, using steady-state precession imaging to obtain a volumetric estimate of SV. Following cMRI, the TBEV SV study was repeated. Comparing the cMRI-derived SV to that of TBEV, the two TBEV estimates were averaged and compared to the cMRI standard. CO was computed as the product of SV and heart rate. Statistical methods consisted of Bland-Altman and linear regression analysis. TBEV SV and CO estimates were obtained in 30 of the 32 subjects enrolled. Bland-Altman analysis of pre- and post-cMRI TBEV SV showed a mean bias of 2.87 % (2.05 mL), precision of 13.59% (11.99 mL) and 95% limits of agreement (LOA) of +29.51% (25.55 mL) and -23.77% (-21.45 mL). Regression analysis for pre- and post-cMRI TBEV SV values yielded y = 0.76x + 25.1 and r(2) = 0.71 (r = 0.84). Bland-Altman analysis comparing cMRI SV with averaged TBEV SV showed a mean bias of -1.56% (-1.53 mL), precision of 13.47% (12.84 mL), 95% LOA of +24.85% (+23.64 mL) and -27.97% (-26.7 mL) and percent error = 26.2 %. For correlation analysis, the regression equation was y = 0.82x + 19.1 and correlation coefficient r(2) = 0.61 (r = 0.78). Bland-Altman analysis of averaged pre- and post-cMRI TBEV CO versus cMRI CO yielded a mean bias of 5.01% (0.32 L min(-1)), precision of 12.85% (0.77 L min(-1)), 95% LOA of +30.20 % (+0.1.83 L min(-1)) and -20.7% (-1.19 L min(-1)) and percent error = 24.8%. Regression analysis yielded y = 0.92x + 0.78, correlation coefficient r(2) = 0.74 (r = 0.86). TBEV is a novel, noninvasive method, which provides satisfactory estimates of SV and CO in normal humans.

Stroke volume obtained by electrical interrogation of the brachial artery: transbrachial electrical bioimpedance velocimetry.

The goal of this study is to measure left ventricular stroke volume (SV) from the brachial artery (BA) using electrical bioimpedance. Doppler-derived SV was used for comparison. Twenty-nine healthy adults were recruited for study. Doppler echocardiographic-derived SV was obtained from the product of distal left ventricular outflow tract cross-sectional area and systolic velocity integral. SV from the BA was obtained by transbrachial electrical bioimpedance velocimetry (TBEV). Application of a current field across the left brachium was effected by injection of a constant magnitude, high frequency, low amperage, alternating current. Therein, a static voltage (U(0)) and pulsatile voltage change (ΔU(t)) were measured and converted to their corresponding impedances, Z(0) and ΔZ(t). TBEV-derived SV was obtained by multiplying a square root value of the normalized, acceleration-based, peak first time derivative of ΔZ(t) by a volume conductor and systolic flow time. Inter-method agreement was determined by the Bland-Altman method. To assess the contribution of blood resistivity variations to ΔZ(t), BA diameters were measured at end-diastole and peak systolic expansion. Results indicate that since the BA demonstrates parabolic, laminar flow, with minimal diameter changes, blood resistivity variations are likely responsible for the derived impedance changes. Bland-Altman analysis shows that SV is obtainable by TBEV from healthy humans at rest.

Stroke volume obtained from the brachial artery using transbrachial electrical bioimpedance velocimetry.

Stroke volume (SV) is the quantity of blood ejected by the cardiac ventricles per each contraction. When SV is multiplied by heart rate, cardiac output is the result. Cardiac output (CO), in conjunction with hemoglobin concentration and arterial oxygen saturation are the cornerstones of oxygen transport. Measurement of CO is important, especially in sick humans suffering from decompensated heart disease and systemic diseases affecting the contractility or loading conditions of the heart. Although reasonably accurate invasive cardiac output methods are available, their use is restricted to those individuals hospitalized in the intensive care units. Thus, a robust noninvasive alternative is considered desirable. Impedance cardiography (ICG) is one such method, but in patients with severe heart disease and/or excess extravascular lung water, the method is inaccurate. This paper concerns the introduction of a new method, transbrachial electrical bioimpedance velocimetry (TBEV). The technique involves passage of a constant magnitude, high frequency, and low amperage ac from the upper arm to the antecubital fossa. In all other respects, the operational aspects of TBEV are consistent with ICG. There is good evidence suggesting that the TBEV waveform and its derivatives are generated by blood resistivity changes only.

Pressure pulse contour-derived stroke volume and cardiac output in the morbidly obese patient.

BACKGROUND: The pressure pulse contour method for measuring stroke volume (SV) and cardiac output (CO) has come of age. Various methods have been proposed, but at this time no single technique has shown clear superiority over the others. This commentary and review discusses the various methods, and particularly the pressure recording analytical method (PRAM). Dissection of the method shows that vascular wall abnormalities, which are not unique to the morbidly obese state, represent one more biophysical perturbation causing inaccuracy in stroke volume and cardiac output determination. As PRAM is an uncalibrated method, its accuracy depends on certain assumptions that may not fully explain the multitude of combinations and permutations that define pulsatile blood flow; specifically, the area under the pressure curve during systole and the morphologic characteristics of the waveform throughout the cardiac cycle. As a result of incomplete theory, referenced specifically to the morbidly obese individual, PRAM does not faithfully mimic established reference standards of flow; it systematically underestimates stroke volume and cardiac output. Field equations, that is, equations that are applicable over the full gamut of hemodynamic conditions and vascular pathology, are analytically derived truisms. They require input variables that satisfy the natural state of affairs. To realize this state of absolute biophysical bliss, these variables should ideally be measured. Unfortunately, because of the constraints of practicality, shortcuts to the absolute truth are obligatorily required. As a result, pressure pulse contour methods have evolved that employ curve analysis and neural networking techniques, providing uncalibrated facsimiles of SV and CO.

Estimating blood volume in obese and morbidly obese patients.

Preoperative assessment of blood volume (BV) is important for patients undergoing surgery. The mean value for indexed blood volume ((In)BV) in normal weight adults is 70 mL/kg. Since (In)BV decreases in a non-linear manner with increasing weight, this value cannot be used for obese and morbidly obese patients. We present an equation that allows estimation of (In)BV over the entire range of body weights.

Estimating ideal body weight--a new formula.

A simple formula for estimating ideal body weight (IBW) in kilograms for both men and women is presented. The equation IBW = 22 x H2, where H is equal to patient height in meters, yields weight values midway within the range of weights obtained using published IBW formulae.

Hemodynamic changes after an intensive short-term exercise and nutrition program in hypertensive and obese patients with and without coronary artery disease / Variações hemodinâmicas após programa intensivo de dieta e exercício hipertensoso obesos com ou sem doença coronária

Purpose: To assess the effectiveness of the Pritikin diet and exercise program on cardiovascular hemodynamics using the noninvasive technique of Thoracic Electrical Bioimpedance (TEB). Material and Methods: Twenty subjects divided in two groups, according to their body habitus and hemodynamic disturbances. These data were compared to a group of 10 healthy individuals not involved in the program. Hemodynamic parameters were collected at admission and at the end of the intensive 26-day program of exercise and nutrition. Results: In obese and hypertensive subjects not on medication we observed that cardiac index increased from 3.27 ± 0.4 to 3.58 ± 0.5 L/min/m2; mean arterial pressure decreased from 100 ± 8.5 to 94.8 ± 7.9 mmHg while systemic vascular resistance index decreased from 2362 ± 391 to 1934 ± 357 dynes. sec. cm-5/m2; p < 0.05 (Data obtained in supine position)...

Objetivo: Avaliar a eficácia da dicta de Pritikin e programa de condicionamento físico pela análise de parâmetros hemodinâmicos obtidos com a técnica não invasiva de Bioimpedância Torácica (BIT). Pacientes e Métodos: Vinte hipertensos obesos foram divididos em dois grupos de acordo com o uso ou não de drogas para coronariopatia e hipertensão arterial. Os dados hemodinâmicos foram obtidos no início e no fim de um programa intensivo de condicionamento (exercício e dieta) com duração de 26 dias. Estes dados foram comparados com os de outro grupo e dez indivíduos normais. Resultados: No grupo de obesos hipertensos não medicados, foi documentuao aumento do índice cardíaco de 3,27 ± 0,4 para 3,58 ± 0,5 L/min/m2, diminuição da pressão arterial média de 100 ± 8,5 para 94,8 ± 7,9 mmHg e queda do índice de resistência vascular periférica de 2362 ± 391 para 1934 ± 357 dyne. seg. cm-5/m2...